Thrust compensation system for fluid transport devices

ABSTRACT

A fluid transport device defining a centerline axis therethrough includes at least one rotatable member including a first portion and a second portion axially opposite the first portion. The fluid transport device also includes at least one stationary member positioned proximate the at least one rotatable member. The at least one rotatable member and the at least one stationary member define at least one stage. The at least one rotatable member defines at least one pressure balance port extending from the second portion to the first portion. The at least one pressure balance port is configured to substantially equalize a fluid pressure proximate the second portion with a pressure of a fluid proximate the first portion.

BACKGROUND

The field of the disclosure relates generally to fluid transport systems and, more particularly, to thrust compensation systems for fluid transport devices.

At least some known fluid transport systems include multistage transport devices, i.e., pumps configured to transport single-phase and multi-phase fluids. In general, such multistage pumps generate large axial thrust forces as a result of the pressure increase that occurs across each of the pump stages. These thrust forces must be compensated by using a balance piston (sometimes referred to as a balance drum) or a thrust bearing, and in some cases, both devices are used. In operation, the thrust forces induced by the pump stages and the thrust compensations devices are in substantial balance. These thrust compensation devices for large thrust forces typically include additional hardware features that increase the capital costs of the pumps and increase the maintenance costs as a function of operational wear over time. Such wear further having the potential for degrading the performance of the pump and potentially decreasing the reliability of the pump system.

Further, at least some of these known pumps are used for oil recovery, e.g., within submersible pumping systems often deployed into oil wells to recover petroleum fluids from subterranean reservoirs, where multiphase fluids, such as gaseous and liquid two-phase fluids exist. Such pumps include helico-axial, mixed flow, and radial pumps configured for pumping gas and liquid mixtures with gas volume fractions between 0% and 100%, where such multiphase fluids, e.g., petroleum-gas-water mixtures, may tend to separate into liquid and gaseous components. Many of such known pumps include one or more impeller and diffuser combinations, commonly referred to as “stages.” The impellers rotate within adjacent stationary diffusers. During use, the rotating impeller imparts kinetic energy to the fluid. A portion of the kinetic energy is converted to pressure as the fluid passes through the downstream diffuser.

As gas volumes, i.e., gas slugs entrained with the liquid portion of the fluid are channeled through each stage of the pump, the pressure differential across the affected stage is changed. Specifically, due to the compressibility of the gas volume, the gas volume flow rate and the associated pressure at the affected stage decrease. However, the thrust compensation devices are compensating for an overall pressure differential across the pump between the inlet and outlet and the compensation devices do not adjust for the decrease in pressure differential for any one stage. Therefore, the impact on the thrust of the individual stages experiencing gas slugging is different than the impact on the overall pump thrust, and the thrust compensation features do not experience the same variation in thrust. As a result, an unbalanced thrust force is induced across the pump because the thrust induced across the affected stages changes but the counter-thrust induced by the compensation features is substantially static. Therefore, overloading of the thrust bearing may develop and the associated service life of the thrust bearing may be decreased.

BRIEF DESCRIPTION

In one aspect, a fluid transport device is provided. The fluid transport device defines a centerline axis therethrough. The fluid transport device includes at least one rotatable member including a first portion and a second portion axially opposite the first portion. The fluid transport device also includes at least one stationary member positioned proximate the at least one rotatable member. The at least one rotatable member and the at least one stationary member define at least one stage. The at least one rotatable member defines at least one pressure balance port extending from the second portion to the first portion. The at least one pressure balance port is configured to substantially equalize a fluid pressure proximate the second portion with a pressure of a fluid proximate the first portion.

In a further aspect, a thrust compensation system is provided. The thrust compensation system includes a rotor shaft defining an axial centerline therethrough. The rotor shaft includes a rotatable hub. The rotatable hub includes an axially upstream hub portion and an axially downstream hub portion axially opposite the axially upstream hub portion. The at least one rotatable hub defines at least one pressure balance port extending from the axially downstream hub portion to the axially upstream hub portion. The at least one pressure balance port is configured to substantially equalize a fluid pressure proximate the axially downstream hub portion with a pressure of a fluid proximate the axially upstream hub portion.

In another aspect, a fluid transport system is provided. The fluid transport system is configured to pump a multiphase fluid. The fluid transport system includes a pump driving mechanism, a fluid conduit, and a helico-axial pump rotatably coupled to the pump driving mechanism and coupled in flow communication with the fluid conduit. The helico-axial pump defines an axial centerline therethrough. The helico-axial pump includes at least one stage including at least one rotatable member including a first portion and a second portion axially opposite the inlet portion. The helico-axial pump also includes at least one stationary member positioned proximate the at least one rotatable member. The at least one rotatable member defines at least one pressure balance port extending from the second portion to the first portion. The at least one pressure balance port is configured to substantially equalize a fluid pressure proximate the second portion with a pressure of a fluid proximate the first portion.

DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a cross-sectional side view of a well assembly having an exemplary fluid transport system;

FIG. 2 is a schematic view of a prior art helico-axial mixed flow pump;

FIG. 3 is a schematic view of an exemplary helico-axial mixed flow pump that may be used with the fluid transport system shown in FIG. 1;

FIG. 4 is a schematic view of an alternative helico-axial mixed flow pump that may be used with the fluid transport system shown in FIG. 1; and

FIG. 5 is a schematic view of another alternative helico-axial mixed flow pump that may be used with the fluid transport system shown in FIG. 1.

Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

As used herein, the numerical values for the various embodiments of this disclosure are illustrative examples and should not be considered as limiting in any manner.

The thrust compensation system, pumping devices, and fluid transport systems as described herein overcome a number of deficiencies associated with known systems and methods of thrust compensation in multi-phase, multistage pumps. Specifically, the thrust compensation systems described herein includes modifications to the pump rotor to provide a partial internal thrust compensation passage, i.e., a pressure balance port for each stage of the pump by managing the pressure on the downstream surface of the rotor disk. A second embodiment of the thrust compensation systems includes using a compensating pressure which spans two or more stages. In addition to extending the pressure balance ports between adjacent stages or other stages to equilibrate the pressure between the upstream and downstream sides of the rotor disk, the effects of decreasing the pressure on the downstream side of the rotor disk is further enhanced by adding a flow seal having a diameter approximately equal to the blade hub diameter on the downstream side of a stage. This seal isolates the higher pressures at the outlet of the associated stages from the pressure balance ports.

These features substantially reduce individual stage thrusts and the resulting overall rotor thrust, thereby facilitating use of smaller thrust compensation devices. More specifically, since the enhanced thrust compensation features described herein reduce the overall thrust generated by the pump, use of smaller balance pistons and thrust bearings is facilitated. Therefore, for pumps operating with variable gas volume fraction, the thrust generated by any given stage or group of stages is substantially reduced, thereby facilitating a more robust response to variable operating conditions. The reduced thrusts and smaller thrust compensation devices facilitate an increased reliability of the pump.

FIG. 1 is a cross-sectional side view of a well assembly 100 including a fluid transport system 102 vertically coupled to a wellbore 104 via a wellhead 106. In the exemplary embodiment, well assembly 100 is shown as a topside assembly. Alternatively, well assembly 100 is used for any multiphase pumping application including, without limitation, a subsea assembly. Fluid transport system 102 includes a pump driving mechanism, i.e., an electric motor 108 rotatably coupled to a helico-axial mixed flow pump 120. Alternatively, rather than an electric drive, motor 108 is any drive device that enables operation of fluid transport system 102 as described herein, including, without limitation, water-driven motors. Fluid transport system 102 is designed for deployment in wellbore 104 within a geological formation 122 containing desirable production fluids 124, such as, but not limited to, multiphase fluids including gas, water, and liquid petroleum mixtures with gas volume fractions between 0% and 100%. Wellbore 104 is drilled into geological formation 122 and lined with a well casing 126. Well casing 126 includes an inner sidewall 128, an outer sidewall 130, a casing bore 132 defined by inner sidewall 128.

Well casing 126 defines a first zone 134 and a second zone 136 therein. In the exemplary embodiment, first zone 134 is vertically located above second zone 136. Alternatively, well casing 126 is positioned in any orientation within geological formation 122 and includes any number of zones in any orientation to enable fluid transport system 102 to function as described herein. A plurality of perforations 138 is formed through well casing 126 to permit fluid 124 to flow into wellbore 114 from geological formation 122 and into second zone 136. Alternatively, perforations 138 are formed through well casing 126 to permit fluid 124 to flow into wellbore 114 from geological formation 122 and into first zone 134.

Well assembly 100 further includes a production string 152 coupled to wellhead 106 and to fluid transport system 102. In the exemplary embodiment, fluid transport system 102 is configured to pump fluid 124 from geological formation 122 to wellhead 106 through wellbore 104, which acts as a conduit.

FIG. 2 is a schematic view of a prior art helico-axial mixed flow pump 200. Pump 200 includes a rotatable member 204 that includes a rotor shaft 206 and an impeller 208 rotatably coupled to rotor shaft 206. Impeller 208 includes a hub 210, a first impeller portion, i.e., an impeller inlet portion 212, a second impeller portion, i.e., an impeller outlet portion 214, and a plurality of impeller vanes 216 (only one shown in FIG. 2) coupled to hub 210 at a hub-vane interface 217. Pump 200 also includes at least one stationary member positioned proximate rotatable member 204, i.e., the at least one stationary member includes a pump casing 218 radially outboard of impeller 208, where casing 218 extends over impeller vanes 216.

Pump 200 further includes a diffuser section 220 positioned downstream of impeller 208. Diffuser section 220 includes a plurality of stationary vanes 222 (only one shown in FIG. 2) coupled to pump casing 218. Stationary vanes 222 extend radially inward toward rotor shaft 206 from pump casing 218. Each stationary vane 222 includes a guide vane 224 and at least one seal member 226 coupled to guide vane 224. Pump casing 218, seal member 226, and guide vane 224 define a fluid flow path, i.e., diffuser outlet region 228 downstream from guide vane 224. Impeller 208 and diffuser section 220 define a pump stage 230 and rotor shaft 206 defines a pump axial centerline 232. Impeller 208, diffuser section 220, and pump casing 218 define impeller outlet portion 214 therebetween, where impeller outlet portion 214 is also a diffuser inlet region.

Seal member 226 includes a plurality of seals, i.e., a first seal 236 and a second seal 238 coupled thereto such that seals 236 and 238 are proximate rotor shaft 206 to facilitate reducing a potential for fluid to flow through a shaft clearance region 240 from higher-pressure impeller outlet portion 214 to lower-pressure impeller outlet portion 214, thereby facilitating increasing an efficiency of pump 200.

In operation, a mixed fluid including gas and liquid mixtures with gas volume fractions between 0% and 100%, and as shown by arrows 242, enters pump stage 230 at impeller inlet portion 212 through an impeller eye (not shown) at a first pressure, or pump inlet pressure P1 of approximately 200,000 Pascal (Pa), i.e., 200 kiloPascal (kPa). Fluid 242 travels through rotating impeller vanes 216 that increase the pressure of fluid 242 to a second pressure, or an impeller outlet pressure P2 of approximately 400 kPa where fluid 242 enters diffuser section 220. Fluid 242 flows around guide vanes 224 and exits pump 200 through diffuser outlet region 228 at a third pressure, or pump outlet pressure P3 of approximately 440 kPa.

Also, in operation, rotor shaft 206 and hub 210 define a first radial length R1 at impeller inlet portion 212 extending from pump axial centerline 232 to hub-vane interface 217, where R1 is approximately 0.08 meters (m). Rotor shaft 206, hub 210, and vane 216 define a second radial length R2 at impeller outlet portion 214 extending from pump axial centerline 232 to a radially outermost portion of vane 216, where R2 is approximately 0.10 m. Rotor shaft 206 and hub 210 define a third radial length R3 at impeller outlet portion 214 extending from pump axial centerline 232 to hub-vane interface 217, where R3 is approximately 0.09 m. R4 is intentionally skipped for now and will be discussed further below. Rotor shaft 206 defines a fifth radial length R5 proximate seal member 226 extending from pump axial centerline 232 to a radially outermost portion of rotor shaft 206, where R5 is approximately 0.06 m.

As such, an acting force F1 on pump stage 230 at impeller inlet portion 212 is represented by the equation F1=P1*π*[R2²−R5²]=4021 Newtons (N) to the right. Similarly, an acting force F2 on pump stage 230 at impeller outlet portion 214 is represented by the equation F2=P2*π*[R2²−R5²]=8042 N to the left, thereby inducing a net force Fnet1 of 4021 N acting to the left on stage 230. Therefore, prior art pump 200 inherently induces axial thrust forces on the rotor as a side effect of the primary purpose in raising the pressure of the fluid being pumped. This axial thrust must be counter-acted with thrust compensation devices including a thrust piston, i.e., a balance drum (not shown) or a thrust bearing (not shown), or most commonly both, to keep the rotor balanced. In multi-stage machines, large thrust forces are generated requiring large thrust compensation devices which negatively impact performance and reliability.

Similarly, for a pump 200 that has a second, identical stage 250 in series with pump stage 230, in operation, a mixed fluid including gas and liquid mixtures with gas volume fractions between 0% and 100%, and as shown by arrows 242, exits first stage 230 through diffuser outlet region 228 at the third pressure P3 of approximately 440 kPa and enters second pump stage 250 at impeller inlet portion 212 through an impeller eye (not shown) at the third pressure. Fluid 242 travels through rotating impeller vanes 216 that increase the pressure of fluid 242 to a fourth pressure, or an impeller outlet pressure P4 of approximately 880 kPa where fluid 242 enters diffuser section 220. Fluid 242 flows around guide vanes 224 and exits pump 200 through diffuser outlet region 228 at a fifth pressure, or second stage outlet pressure P5 of approximately 968 kPa.

Also, in operation, first radial length R1, second radial length R2, third radial length R3, and fifth radial length R5 in second pump stage 250 are substantially similar to those in first stage 230. As such, an acting force F3 on pump stage 250 at impeller inlet portion 212 is represented by the equation F3=P3*π*[R2²−R5²]=8847 Newtons (N) to the right. Similarly, an acting force F4 on pump stage 250 at impeller outlet portion 214 is represented by the equation F4=P5*π*[R2²−R5²]=17,693 N to the left, thereby inducing a net force Fnet2 of 8847 N acting to the left on stage 250. The total net forces induced by first stage 230 and second stage 250 are 4021 N plus 8846 N=12,867 N to the left. Therefore, as described above, as the number of stages on prior art pump 200 increases, the induced axial thrust forces on the rotor as a side effect of the primary purpose in raising the pressure of the fluid being pumped increase. As such, for multistage pumps, these axial thrusts must be counter-acted with even larger and/or additional thrust compensation devices.

FIG. 3 is a schematic view of an exemplary fluid transport device, i.e., helico-axial mixed flow pump 300 that may be used with fluid transport system 102 (shown in FIG. 1) in place of pump 120 (shown in FIG. 1). Pump 300 includes a rotatable member 304 that includes a rotor shaft 306 and an impeller 308 rotatably coupled to rotor shaft 306. Impeller 308 includes a hub 310 and a first, or an axially upstream portion 311 that includes an impeller inlet portion 312. Impeller 308 also includes a second, or an axially downstream portion 313 that includes an impeller outlet portion 314. Impeller 308 further includes a plurality of impeller vanes 316 (only one shown in FIG. 3) coupled to hub 310 at a hub-vane interface 317. Pump 300 also includes at least one stationary member positioned proximate rotatable member 304, i.e., the at least one stationary member includes a pump casing 318 radially outboard of impeller 308, where casing 318 extends over impeller vanes 316.

Pump 300 further includes a diffuser section 320 positioned downstream of impeller 308. Diffuser section 320 includes a plurality of stationary vanes 322 (only one shown in FIG. 3) coupled to pump casing 318. Stationary vanes 322 extend radially inward toward rotor shaft 306 from pump casing 318. Each stationary vane 322 includes a guide vane 324 and at least one seal member 326 coupled to guide vane 324. Pump casing 318, seal member 326, and guide vane 324 define a fluid flow path, i.e., a diffuser outlet region 328 downstream from guide vane 324. Impeller 308 and diffuser section 320 define a pump stage 330 and rotor shaft 306 defines a pump axial centerline 332. Impeller 308, diffuser section 320, and pump casing 318 at least partially define second, or axially downstream portion 313 including impeller outlet portion 314 therebetween, where a portion of impeller outlet portion 314 is also a diffuser inlet region.

In operation, a mixed fluid including gas and liquid mixtures with gas volume fractions between 0% and 100%, and as shown by arrows 342, enters pump stage 330 at impeller inlet portion 312 through an impeller eye (not shown) at a first pressure, or pump inlet pressure P1 of approximately 200 kPa. Fluid 342 travels through rotating impeller vanes 316 that increase the pressure of fluid 342 to a second pressure, or an impeller outlet pressure P2 of approximately 400 kPa where fluid 242 enters diffuser section 320. Fluid 342 flows around guide vanes 324 and exits pump 300 through diffuser outlet region 328 at a third pressure, or pump outlet pressure P3 of approximately 440 kPa.

In the exemplary embodiment, helico-axial mixed flow pump 300 includes a thrust compensation system 334. Thrust compensation system 334 includes seal member 326 that includes a plurality of seals, i.e., a first seal 336 and a second seal 338 coupled thereto. Thrust compensation system 334 includes a first seal extension 350 integrally coupled to hub 310 on its downstream side proximate seal member 326, i.e., first seal extension 326 is within axially downstream portion 313. Thrust compensation system 334 also includes a second seal extension 352 integrally coupled to seal member 326 extending axially upstream toward first seal extension 350 within axially downstream portion 313. First seal 336 is coupled to second seal extension 352 such that seal 336 is proximate first seal extension 350 to reduce a clearance between second seal extension 352 and first seal extension 350. Second seal 338 is coupled to seal member 326 such that seal 338 is proximate rotor shaft 306 to facilitate reducing a potential for fluid to flow through a clearance between seal member 326 and shaft rotor 306. Seals 336 and 338, shaft rotor 306, seal member 326, and first seal extension 350 define a pressure balance cavity 354 within axially downstream portion 313. As such, thrust compensation system 334 includes pressure balance cavity 354.

Also, in the exemplary embodiment, thrust compensation system 334 includes at least one pressure balance port 356 (only one shown in FIG. 3) that is defined within hub 310 such that pressure balance port 356 extends from pressure balance cavity 354 proximate the downstream side of hub 310 within axially downstream portion 313 to impeller inlet portion 312 proximate the upstream side of hub 310 within axially upstream portion 311. Pressure balance port 356, first seal extension 350, second seal extension 352, and seals 336 and 338 cooperate to substantially reduce a potential for fluid at pressures P2 and P3, respectively, to leak into pressure balance cavity 354 which is maintained in substantial equilibrium with impeller inlet portion 312 at a pressure of approximately P1.

Further, in the exemplary embodiment, rotor shaft 306 and hub 310 define a first radial length R1 at impeller inlet portion 312 extending from pump axial centerline 332 to hub-vane interface 317, where R1 is approximately 0.08 m. Rotor shaft 306, hub 310, and vane 316 define a second radial length R2 at impeller outlet portion 314 extending from pump axial centerline 232 to a radially outermost portion of vane 316, where R2 is approximately 0.10 m. Rotor shaft 306 and hub 310 define a third radial length R3 at impeller outlet portion 314 extending from pump axial centerline 332 to hub-vane interface 317, where R3 is approximately 0.09 m. R4 is intentionally skipped for now and will be discussed further below. Rotor shaft 306 defines a fifth radial length R5 proximate seal member 326 extending from pump axial centerline 332 to a radially outermost portion of rotor shaft 306, where R5 is approximately 0.06 m.

In operation, an acting force F1 on pump stage 330 at impeller inlet portion 312 is represented by the equation F1=P1*π*[R2²−R5²]=4021 Newtons (N) to the right. Similarly, an acting force F2 on pump stage 330 at axial downstream portion 313 is represented by the equation F2=P2*π*[R2²−R5²]+P1*π*[R3²−R5²]=2388 N+2827 N=5215 N to the left, thereby inducing a net force Fnet of 1194 N acting to the left on stage 330, which is significantly less than net force Fnet1 of 4021 N acting to the left on stage 230 (shown in FIG. 2).

Therefore, thrust compensation system 334 modifies the design of the pump rotor to provide a partial internal thrust compensation for each stage of a multi-stage pump by managing the pressure on the downstream surface of the rotor disk. Utilizing this feature substantially reduces individual stage thrust and resulting overall rotor thrust, thereby facilitating use of smaller thrust compensation devices. Therefore, thrust compensation system 334 facilitates lowering the pressure on the downstream side of the rotor disk by adding a flow seal at a radial distance from the rotor centerline approximately equal to the blade hub diameter and introducing a balance port to equilibrate the pressure between the upstream and downstream sides of the disk. In addition, the variable thrust effects induced by the variation as the gas volume fractions within the fluid being pumped fluctuate between 0% and 100% are mitigated since thrust compensation system 334 provides thrust compensation for each stage or group of stages making the pumps more robust to variable operating conditions.

FIG. 4 is a schematic view of an alternative fluid transport device, i.e., helico-axial mixed flow pump 400 that may be used with fluid transport system 102 (shown in FIG. 1) in place of pump 120 (shown in FIG. 1). Pump 400 includes a rotatable member 404 that includes a rotor shaft 406 and a plurality of impellers (discussed further below) rotatably coupled to rotor shaft 406. Pump 400 further includes a pump casing 418, a pump axial centerline 432, an alternative thrust compensation system 434, and flows 442. Pump 400 also includes a first stage 460 that is similar to stage 230 (shown in FIG. 2) and a second stage 462 that is similar to stage 330 (shown in FIG. 3), where first stage 460/230 and second stage 462/330 are in serial communication. First stage 460 includes a first stage impeller 464 and second stage 462 includes a second stage impeller 466, where both impellers 464 and 466 are coupled to rotor shaft 406 through a first stage hub 468 and a second stage hub 470, respectively. Further, first stage 460 includes a first hub-vane interface 472 and second stage 474 includes a second stage hub-vane interface 480. First stage hub 468 and second stage hub 470 are coupled at an annular joint 476. Accordingly, first stage 460 includes a first stage diffuser section 478 and second stage 462 includes a second stage diffuser section 480. Moreover, pump 400 also includes a first, or an axially upstream portion 481 that includes a first impeller inlet portion 482, a first impeller outlet portion 484 (that is also a first diffuser inlet region), a first diffuser outlet region 486 (that is also a second impeller inlet portion), a second impeller outlet portion 488 (that is also a second diffuser inlet region), and a second diffuser outlet region 490.

In this alternative embodiment, thrust compensation system 434 is similar to thrust compensation system 334 (shown in FIG. 3) with system 434 including at least one pressure balance port 492 (only one shown in FIG. 4) that is defined within hubs 468 and 470 such that pressure balance port 492 extends from pressure balance cavity 354 proximate second impeller outlet portion 488 to impeller inlet portion 482 proximate axially upstream portion 481, thereby extending through two stages. Alternatively, pressure balance port 492 extends through any number of stages that enables operation of pump 400 and fluid transport system 102 as described herein.

In operation, a mixed fluid including gas and liquid mixtures with gas volume fractions between 0% and 100%, and as shown by arrows 442, enters first pump stage 460 at first impeller inlet portion 482 through an impeller eye (not shown) at a first pressure, or pump inlet pressure P1 of approximately 200 kPa. Fluid 442 travels through first stage 460 that increases the pressure of fluid 442 to a second pressure P2 of approximately 400 kPa at first impeller outlet portion 484 and fluid 442 exits first stage 460 through first diffuser outlet region 228 at a third pressure P3 of approximately 440 kPa. Fluid 442 enters second stage 462 at third pressure P3 of approximately 440 kPa and second stage 462 increases the pressure of fluid 442 to a fourth pressure P4 of approximately 880 kPa at second impeller outlet portion 488 and fluid 442 exits pump 400 through second diffuser outlet region 428 at a fifth pressure P5 of approximately 968 kPa. As such, second stage 462 includes seals 436 and 438 that are similar to seals 336 and 338, respectively (both shown in FIG. 3), where seals 436 and 438 are more robust to seal against the significantly higher pressures. Also, in this alternative embodiment, thrust compensation system 434 includes pressure balance port 456 that facilitates maintaining pressure balance cavity 354 in substantial equilibrium with impeller inlet portion 482 at a pressure of approximately P1.

Also, in this alternative embodiment, rotor shaft 406 and first hub 468 define a first radial length R1 at first impeller inlet portion 482 extending from pump axial centerline 432 to hub-vane interface 472, where R1 is approximately 0.08 m. Rotor shaft 406, hub 468, and vane 216 define a second radial length R2 extending from pump axial centerline 432 to a radially outermost portion of vanes 216 and 316, where R2 is approximately 0.10 m. Rotor shaft 406 and hub 468 define a third radial length R3 at first impeller outlet portion 484 extending from pump axial centerline 432 to a hub-to-seal member interface 494, where R3 is approximately 0.07 m. A fourth radial length R4 at second impeller outlet portion 488 extends from pump axial centerline 432 to first seal 336, where R4 is approximately 0.09 m. Rotor shaft 406 defines a fifth radial length R5 proximate seal member 326 extending from pump axial centerline 432 to a radially outermost portion of rotor shaft 406, where R5 is approximately 0.06 m.

As such, in operation, an acting force F1 on pump stage 460 at impeller inlet portion 482 is represented by the equation F1=P1*π*[R2²−R5²]+P3*π*[R2²−R3²]=4021 N+7050 N=11,071 N to the right. Similarly, an acting force F2 on pump stage 460 at first impeller outlet portion 484 is represented by the equation F2=P2*π*[R2²−R3²]=6409 N to the left. Similarly, an acting force F3 on pump stage 462 at second impeller outlet portion 488 is represented by the equation F3=P4*π*[R2²−R4²]+P1*π*[R4²−R5²]=5253 N+2827 N=8080 N to the left. A net force Fnet of 3418 N is induced as acting to the left, which is significantly less than net force Fnet2 of 12,867 N acting to the left on two-stage pump 200 (shown in FIG. 2).

FIG. 5 is a schematic view of another alternative fluid transport device, i.e., helico-axial mixed flow pump 500 that may be used with fluid transport system 102 (shown in FIG. 1) in place of pump 120 (shown in FIG. 1). Pump 500 includes a rotatable member 504 that includes a rotor shaft 506 and a plurality of impellers (discussed further below) rotatably coupled to rotor shaft 506. Pump 500 further includes a pump casing 518, a pump axial centerline 532, an alternative thrust compensation system 534, and flows 542. Pump 500 also includes a first stage 560 that is similar to stage 330 (shown in FIG. 3) and a second stage 562 that is also similar to stage 330, where first stage 560/330 and second stage 562/330 are in serial communication. First stage 560 includes a first seal member 563 and a first stage impeller 564. Second stage 562 includes a second seal member 565 and a second stage impeller 566. Both impellers 564 and 566 are coupled to rotor shaft 506 through a first stage hub 568 and a second stage hub 570, respectively. Both seal members 563 and 565 are similar to seal member 326 (shown in FIGS. 3 and 4). Further, first stage 560 includes a first hub-vane interface 572 and second stage 574 includes a second stage hub-vane interface 580. First stage hub 568 and second stage hub 570 are coupled at an annular joint 576. Accordingly, first stage 560 includes a first stage diffuser section 578 and second stage 562 includes a second stage diffuser section 580. Moreover, pump 500 also includes a first, or an axially upstream portion 581 that includes a first impeller inlet portion 582, a first impeller outlet portion 584 (that is also a first diffuser inlet region), a first diffuser outlet region 586 (that is also a second impeller inlet portion), a second impeller outlet portion 588 (that is also a second diffuser inlet region), and a second diffuser outlet region 590.

In this alternative embodiment, thrust compensation system 534 is similar to thrust compensation system 434 (shown in FIG. 4) with system 534 including at least two pressure balance ports 592 and 593 (only one of each shown in FIG. 5). Pressure balance port 592 is similar to pressure balance port 356 (shown in FIG. 3). Pressure balance port 592 is defined within first hub 568 such that pressure balance port 592 extends from a first pressure balance cavity 594 proximate first impeller outlet portion 584 to impeller inlet portion 582 proximate axially upstream portion 581, thereby extending through one stage. Pressure balance port 593 is similar to pressure balance port 492 (shown in FIG. 4). Pressure balance port 593 is define within second hub 470 such that pressure balance port 593 extends from a second balance cavity 595 proximate second impeller outlet portion 590 to impeller inlet portion 582 proximate axially upstream portion 581, thereby extending through two stages. Alternatively, pressure balance ports 592 and 593 extend through any number of stages that enables operation of pump 500 and fluid transport system 102 described herein.

In operation, a mixed fluid including gas and liquid mixtures with gas volume fractions between 0% and 100%, and as shown by arrows 542, enters first pump stage 560 at first impeller inlet portion 582 through an impeller eye (not shown) at a first pressure, or pump inlet pressure P1 of approximately 200 kPa. Fluid 542 travels through first stage 560 that increases the pressure of fluid 542 to a second pressure P2 of approximately 400 kPa at first impeller outlet portion 582 and fluid 542 exits first stage 560 through first diffuser outlet region 586 at a third pressure P3 of approximately 440 kPa. Fluid 542 enters second stage 562 at third pressure P3 of approximately 440 kPa and second stage 562 increases the pressure of fluid 542 to a fourth pressure P4 of approximately 880 kPa at second impeller outlet portion 588 and fluid 542 exits pump 400 through second diffuser outlet region 528 at a fifth pressure P5 of approximately 968 kPa. As such, first stage 560 includes seals 336 and 338 and second stage 562 includes seals 436 and 438 that are similar to seals 336 and 338, respectively, where seals 436 and 438 are more robust to seal against the significantly higher pressures. Also, in this alternative embodiment, thrust compensation system 534 includes pressure balance ports 592 and 593 that facilitate maintaining pressure balance cavities 594 and 595 in substantial equilibrium with impeller inlet portion 582 at a pressure of approximately P1.

Also, in this alternative embodiment, rotor shaft 506 and first hub 568 define a first radial length R1 at first impeller inlet portion 582 extending from pump axial centerline 532 to hub-vane interface 572, where R1 is approximately 0.08 m. Rotor shaft 506, hub 568, and vane 316 define a second radial length R2 extending from pump axial centerline 532 to a radially outermost portion of vanes 316, where R2 is approximately 0.10 m. Rotor shaft 506 and hub 568 define a third radial length R3 at first impeller outlet portion 584 extending from pump axial centerline 532 to a hub-to-seal member interface 596, where R3 is approximately 0.07 m. A fourth radial length R4 at first and second impeller outlet portions 584 and 588, respectively, extend from pump axial centerline 532 to first seals 336 and 436, respectively, where R4 is approximately 0.09 m. Rotor shaft 506 defines a fifth radial length R5 proximate seal members 563 and 565 extending from pump axial centerline 532 to a radially outermost portion of rotor shaft 506, where R5 is approximately 0.06 m.

As such, in operation, an acting force F 1 on pump stage 560 at impeller inlet portion 582 is represented by the equation F1=P1*π*[R2²−R5²]+P3*π*[R2²−R3²]=4021 N+7050 N=11,071 N to the right. Similarly, an acting force F2 on pump stage 560 at first impeller outlet portion 584 is represented by the equation F2=P2*π*[R2²−R3²]+P1*π*[R4²−R3²]=2388 N+2011 N to the left. Similarly, an acting force F3 on pump stage 562 at second impeller outlet portion 588 is represented by the equation F3=P4*π*[R2²−R4²]+P1*π*[R4²−R5²]=5253 N+2827 N=8080 N to the left. A net force Fnet of 1408 N is induced as acting to the left, which is significantly less than net force Fnet2 of 12,867 N acting to the left on two-stage pump 200 (shown in FIG. 2).

The above described thrust compensation system, pumping devices, and fluid transport systems overcome a number of deficiencies associated with known systems and methods of trust compensation in multi-phase, multistage pumps. Specifically, the thrust compensation systems described herein includes modifications to the pump rotor to provide a partial internal thrust compensation passage, i.e., a pressure balance port for each stage of the pump by managing the pressure on the downstream surface of the rotor disk. A second embodiment of the thrust compensation systems includes using a compensating pressure which spans two or more stages. In addition to extending the pressure balance ports between adjacent stages or other stages to equilibrate the pressure between the upstream and downstream sides of the rotor disk, the effects of decreasing the pressure on the downstream side of the rotor disk is further enhanced by adding a flow seal having a diameter approximately equal to the blade hub diameter on the downstream side of a stage. This seal isolates the higher pressures at the outlet of the associated stages from the pressure balance ports.

These features substantially reduce individual stage thrusts and the resulting overall rotor thrust, thereby facilitating use of smaller thrust compensation devices. More specifically, since the enhanced thrust compensation features described herein reduce the overall thrust generated by the pump, use of smaller balance pistons and thrust bearings is facilitated. Therefore, for pumps operating with variable gas volume fraction, the thrust generated by any given stage or group of stages is substantially reduced, thereby facilitating a more robust response to variable operating conditions. The reduced thrusts and smaller thrust compensation devices facilitate an increased reliability of the pump.

An exemplary technical effect of the methods, systems, and apparatus described herein includes at least one of: (a) decreasing the differential pressure across stages in a helico-axial pump in the non-flow path portions, thereby decreasing the thrust induced across the associated stages; (b) decreasing the pressure on the downstream side of at least a portion of each pump stage, thereby decreasing the thrust induced across the associated stages; (c) decreasing the overall thrust induced by the stages, individually and cumulatively, thereby facilitating smaller thrust compensation devices such as thrust bearings and balance drums; and (d) facilitating a more robust response to variable operating conditions for pumps operating with variable gas volume fraction.

Exemplary embodiments of thrust compensation systems, pumping devices, and fluid transport systems are described above in detail. The thrust compensation systems, pumping devices, and fluid transport systems, and methods of operating such systems and devices are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the systems, apparatus, and methods may also be used in combination with other systems requiring features to reduce thrusts induced across the stages of multi-stage fluid compression and pressure-increasing devices, and are not limited to practice with only the pumps, systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other multiphase fluid pressure-increasing applications that are configured to transport fluids, e.g., and without limitation, compressors and subsea wells.

Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A fluid transport device defining an axial centerline therethrough, said fluid transport device comprising: at least one rotatable member comprising a first portion and a second portion axially opposite said first portion; and at least one stationary member positioned proximate said at least one rotatable member, wherein said at least one rotatable member and said at least one stationary member define at least one stage, said at least one rotatable member defining at least one pressure balance port extending from said second portion to said first portion, said at least one pressure balance port configured to substantially equalize a fluid pressure proximate said second portion with a pressure of a fluid proximate said first portion.
 2. The fluid transport device in accordance with claim 1, wherein said fluid transport device comprises a single stage.
 3. The fluid transport device in accordance with claim 1, wherein said fluid transport device is a multi-stage fluid transport device comprising: a first stage comprising a first rotatable member and a first stationary member, said first rotatable member comprising a first inlet portion and a first outlet portion axially opposite said first inlet portion; and a second stage comprising a second rotatable member and a second stationary member, said second stage positioned downstream of said first stage, said second rotatable member comprising a second inlet portion and a second outlet portion axially opposite said second inlet portion, said at least one pressure balance port comprising one or more of: a pressure balance port extending between said second outlet portion and said first inlet portion; a pressure balance port extending between said second outlet portion and said second inlet portion; and a pressure balance port extending between said first outlet portion and said first inlet portion.
 4. The fluid transport device in accordance with claim 1, wherein: said at least one rotatable member comprises: a rotor shaft; and at least one impeller comprising at least one hub coupled to said rotor shaft, wherein said first portion comprises an at least one impeller inlet portion and said second portion comprises an at least one impeller outlet portion; and said at least one stationary member comprises: a casing radially outboard of said at least one impeller, said casing extending over said at least one impeller; and at least one stationary vane coupled to said casing, said at least one stationary vane extending radially inward toward said rotor shaft from said casing.
 5. The fluid transport device in accordance with claim 4, wherein said at least one stationary vane comprises at least one guide vane and at least one seal member coupled to said at least one guide vane, said casing and said at least one seal member at least partially define a fluid flow path downstream from said at least one impeller outlet portion.
 6. The fluid transport device in accordance with claim 5, wherein said at least one seal member, said at least one hub, and said rotor shaft at least partially define a pressure balance cavity coupled in flow communication with said at least one impeller inlet portion through said at least one pressure balance port.
 7. The fluid transport device in accordance with claim 6, wherein: said at least one impeller outlet portion comprises a first seal extension; and said at least one seal member comprises at least one second seal extension comprising at least one first seal configured to reduce a clearance between said at least one second seal extension and said at least one first seal extension.
 8. The fluid transport device in accordance with claim 7, wherein said at least one seal member further comprises at least one second seal configured to reduce a clearance between said at least one seal member and said rotor shaft.
 9. A thrust compensation system comprising a rotor shaft defining an axial centerline therethrough, said rotor shaft comprising a rotatable hub, said rotatable hub comprising an axially upstream hub portion and an axially downstream hub portion axially opposite said axially upstream hub portion, said at least one rotatable hub defining at least one pressure balance port extending from said axially downstream hub portion to said axially upstream hub portion, said at least one pressure balance port configured to substantially equalize a fluid pressure proximate said axially downstream hub portion with a pressure of a fluid proximate said axially upstream hub portion.
 10. The thrust compensation system in accordance with claim 9 further comprising at least one seal member positioned proximate said axially downstream hub portion.
 11. The thrust compensation system in accordance with claim 10 further comprising a rotor shaft coupled to said rotatable hub, wherein said rotatable hub comprises a first seal extension, said at least one seal member comprises at least one second seal extension comprising at least one first seal configured to reduce a clearance between said at least one second seal extension and said at least one first seal extension.
 12. The thrust compensation system in accordance with claim 11, wherein said at least one seal member further comprises at least one second seal configured to reduce a clearance between said at least one seal member and said rotor shaft.
 13. The thrust compensation system in accordance with claim 12, wherein said at least one seal member, said at least one hub, and said rotor shaft at least partially define a pressure balance cavity coupled in flow communication with said at least one axially upstream hub portion through said at least one pressure balance port.
 14. A fluid transport system configured to pump a multiphase fluid, said fluid transport system comprising: a pump driving mechanism; a fluid conduit; and a helico-axial pump rotatably coupled to said pump driving mechanism and coupled in flow communication with said fluid conduit, said helico-axial pump defining an axial centerline therethrough, said helico-axial pump comprising at least one stage comprising: at least one rotatable member comprising a first portion and a second portion axially opposite said inlet portion; and at least one stationary member positioned proximate said at least one rotatable member, said at least one rotatable member defining at least one pressure balance port extending from said second portion to said first portion, said at least one pressure balance port configured to substantially equalize a fluid pressure proximate said second portion with a pressure of a fluid proximate said first portion.
 15. The fluid transport system in accordance with claim 14, wherein said helico-axial pump is a multi-stage fluid transport device comprising: a first stage comprising a first rotatable member and a first stationary member, said first rotatable member comprising a first inlet portion and a first outlet portion axially opposite said first inlet portion; and a second stage comprising a second rotatable member and a second stationary member, said second stage positioned downstream of said first stage, said second rotatable member comprising a second inlet portion and a second outlet portion axially opposite said second inlet portion, said at least one pressure balance port comprising one or more of: a pressure balance port extending between said second outlet portion and said first inlet portion; a pressure balance port extending between said second outlet portion and said second inlet portion; and a pressure balance port extending between said first outlet portion and said first inlet portion.
 16. The fluid transport system in accordance with claim 14, wherein: said at least one rotatable member comprises: a rotor shaft; and at least one impeller comprising at least one hub coupled to said rotor shaft, wherein said first portion comprises an at least one impeller inlet portion and said second portion comprises an at least one impeller outlet portion; and said at least one stationary member comprises: a casing radially outboard of said at least one impeller, said casing extending over said at least one impeller; and at least one stationary vane coupled to said casing, said at least one stationary vane extending radially inward toward said rotor shaft from said casing.
 17. The fluid transport system in accordance with claim 16, wherein said at least one stationary vane comprises at least one guide vane and at least one seal member coupled to said at least one guide vane, said casing and said at least one seal member at least partially define a fluid flow path downstream from said at least one impeller outlet portion.
 18. The fluid transport system in accordance with claim 17, wherein said at least one seal member, said at least one hub, and said rotor shaft at least partially define a pressure balance cavity coupled in flow communication with said at least one impeller inlet portion through said at least one pressure balance port.
 19. The fluid transport system in accordance with claim 19, wherein: said at least one impeller outlet portion comprises a first seal extension; and said at least one seal member comprises at least one second seal extension comprising at least one first seal configured to reduce a clearance between said at least one second seal extension and said at least one first seal extension.
 20. The fluid transport system in accordance with claim 19, wherein said at least one seal member further comprises at least one second seal configured to reduce a clearance between said at least one seal member and said rotor shaft. 